The problem with the change in language is that it removes and replaces the current well understood meanings of man/woman, male/female, girl/boy, making it very difficult to then talk about issues that affect one sex more than another.
In the short to medium term I can see there are complications that arise from the whole notion of incorporating trans into our world view. Absolutely it makes it more difficult to find the words. Does that mean it isn't worth overcoming that, given that over time it will almost certainly get easier? Not sure.
If you can't address the concerns that people keep bringing up, just ignore them!
Not sure what you're referencing exactly.
Why can't trans be celebrated?
I don't know, I really don't know. But my limited experience with transpeople is that their journey is one of seeking acceptance in a particular identity, and that identity is not one of having been something else first, it's of having always been that thing but with a body which does not correlate. The idea of feeling that way, to me, is beyond imagining. It's beyond logic to me to feel one's body "does not correlate" - because to me my body is me and I am it... But that's me. I can see why celebrating "used to be that, now this" is not the same thing as "is this, has always been this, body either does not correlate or has undergone medical treatment in an attempt to correlate, but still this".
Yes of course they do, if it’s something manmade, like “marriage”. But if it’s just something immutable like “dog” or “water” or “stone” or “woman” then no they don’t.
Of course those things are immutable, but the terms used to describe them are man-made - necessarily man-made. As is all language, categorisation, measurement etc. These terms describe the reality of things, but the descriptors are not real things in and of themselves. (Sorry, got a bit fluffy with my language there, but this is my dissertation subject so it all comes flooding back...)